ELECTRON-TRANSFER AND ION-PAIR FORMATION .40. SINGLE-CRYSTAL STRUCTURE OF BIS(SODIUM 1,1'-BIPHENYL-2-THIOLATE-DIGLYME) - AN INTERMEDIATE IN THE REDUCTIVE RING-OPENING OF DIBENZOTHIOPHENE

On Na-metal reduction of dibenzothiophene, the five-membered sulfur ring opens to form a colorless 1,1'-biphenyl-2-thiolate sodium salt, which, according to its single-crystal structure determination, is a dimer containing a four-membered, twice diglyme-solvated ring (diglyme...Na(+-)SR)(2). Additional measurements provide the following information: cyclic voltammetry in aprotic MeCN solution shows one quasi-reversible electron transfer at E(1/2)(Red) = -2.58 V. The dibenzothiophene radical anion can be generated in aprotic THF solution at a K mirror and characterized by an 81-line ESR spectrum and its simulation. This blue species is also the first UV/VIS detectable one before the solution changes via green (due to blue + yellow color mixing) to yellow, yielding across an isosbestic point a second and diamagnetic compound. All of the above results suggest a consecutive two-electron reduction followed by an intersystem protonation, M + (e(-)) --> M(.-) (blue) + (e(-)) --> (M(--), yellow?) + (H+) --> MH(-) (colorless), to yield the crystallized and structurally characterized reaction intermediate. The diglyme-solvated sodium-salt dimer provides a basis for a quantum-chemical discussion of some facets of the most likely microscopic reduction pathway.